1. Field of the Disclosure
The present disclosure relates to a keyless entry apparatus that performs predetermined control such as locking/unlocking of the door of a vehicle through mutual communication between a vehicle-side device and a mobile device.
2. Description of the Related Art
In the keyless entry apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2010-185186, a vehicle-side device transmits a request signal having a strength variation to a mobile device. The mobile device, which detects whether or not the request signal has a strength variation, does not send an answer signal when the request signal has no strength variations and sends an answer signal when the request signal has a strength variation. As a result, the simple configuration allows a relay attack to be detected.
Note that a relay attack is performed by a first unauthorized relay device arranged near a vehicle and a second unauthorized relay device which is arranged at a location spaced apart from the vehicle and performs wireless communication with the first relay device. In other words, in the vicinity of the vehicle, a request signal formed of an LF signal transmitted from the vehicle-side device is relayed by the first relay device and the second relay device, and the signal is transmitted from the second relay device. When a person having a mobile device approaches the second relay device, the mobile device will receive a signal relayed by the second relay device. Here, when the mobile device transmits an answer signal formed of an RF signal in accordance with the receipt of the signal relayed by the two relay devices, the vehicle will perform an unlocking operation at a location that is not intended by a user in a state in which the user is spaced apart from the vehicle.
In the keyless entry apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2010-185186, a strength variation is added to a request signal and it is determined whether or not an answer signal is allowed to be transmitted on the basis of whether or not the strength variation exists. However, in the case where the communication status between the vehicle-side device and the mobile device is unstable, or in the case where an apparatus radiating a radio wave such as a cellular phone exists near the mobile device, there may be a case in which it is difficult to keep the strength variation added by the vehicle-side device as is. Hence, in circumstances like this, there may be a case in which the existence of a strength variation cannot be accurately detected on the mobile device side and, hence, it cannot be said that this method has sufficient security capabilities.
Further, in recent years, unauthorized relay devices used for a relay attack have an increased performance and some of newly available devices generate a signal following the strength variation added to a request signal. Hence, it is difficult to prevent a relay attack by only adding a strength variation to a request signal and, hence, there is a problem in that the security is weak.